This invention relates generally to device structures and a method for their fabrication, and more specifically to semiconductor structures and devices and to the fabrication and use of semiconductor structures, devices, and integrated circuits.
Semiconductor devices often include multiple layers of conductive, insulating, and semiconductive layers. Often, the desirable properties of such layers improve with the crystallinity of the layer. For example, the electron mobility and electron lifetime of semiconductive layers improve as the crystallinity of the layer increases. Similarly, the free electron concentration of conductive layers and the electron charge displacement and electron energy recoverability of insulative or dielectric films improve as the crystallinity of these layers increases.
For many years, attempts have been made to grow various monolithic thin films on a foreign substrate such as silicon (Si). To achieve optimal characteristics of the various monolithic layers, however, a monocrystalline film of high crystalline quality is desired. Attempts have been made, for example, to grow various monocrystalline layers on a substrate such as germanium, silicon, and various insulators. These attempts have generally been unsuccessful because lattice mismatches between the host crystal and the grown crystal have caused the resulting layer of monocrystalline material to be of low crystalline quality.
If a large area thin film of high quality monocrystalline material were available at low cost, a variety of semiconductor devices could advantageously be fabricated in or using that film at a low cost compared to the cost of fabricating such devices beginning with a bulk wafer of semiconductor material or in an epitaxial film of such material on a bulk wafer of semiconductor material. In addition, if a thin film of high quality monocrystalline material could be realized beginning with a bulk wafer such as a silicon wafer, an integrated device structure could be achieved that took advantage of the best properties of both the silicon and the high quality monocrystalline material.
Within the past couple of years, various inventive breakthroughs have addressed a need for a semiconductor structure that provides a high quality monocrystalline film or layer over another monocrystalline material and for a process for making such a structure. While these inventive breakthroughs offer significant advantages, it is also true that in many cases silicon is an undesirable substrate for the monocrystalline oxide device. For example, surface acoustic wave (xe2x80x9cSAWxe2x80x9d) devices are preferably fabricated on diamond substrates because of diamond""s high acoustic velocity, and tunable barium strontium titanate (xe2x80x9cBSTxe2x80x9d) and superconducting devices for radio frequency (xe2x80x9cRFxe2x80x9d) applications are preferably fabricated on high quality insulating substrates like sapphire to reduce lossesxe2x80x94even high resistivity silicon will introduce significant losses at RF frequencies. Accordingly, there is a need for a method of fabricating such monocrystalline oxide devices on non-silicon substrates, while at the same time preserving the epitaxial advantages of the silicon wafer, and the ability to integrate such devices with silicon devices. Moreover, it would be highly desirable to integrate monocrystalline oxide devices with silicon-on-insulator (SOI) devices that can operate in fully depleted mode.